Help with TV-Capture

Hi, I'm posting this because I just don't know what to do next with my TV capture card.

It's a cheap-o card, but has a Philips 713x chipset, which I thought would make it okay. However, when I use WinDVR in conjunction with either the S-Video or Composite inputs, I get a 'stuttery', low quality picture. Whichever one I choose the problem is the same.

I'm looking to record some old video tapes to my PC for editing and DVD'ing, but at the moment there's no way I can.

BTW, I got an external digital TV tuner to work fine through the card, so surely there can't be any problem with it (??).

Thanks for any help in advance.

I'm capturing MPEG-1 352x288 CBR. It's just about the lowest setting you can get. It's running on a Sempron 2200+ with 640mb of DDR333 and a Radeon 9200 64mb graphics card. Surely even that spec can encode realtime MPEG-1??